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Re: [Qemu-devel] [PATCH v1 for 3.0 1/2] linux-user/mmap.c: handle len =


From: Alex Bennée
Subject: Re: [Qemu-devel] [PATCH v1 for 3.0 1/2] linux-user/mmap.c: handle len = 0 maps correctly
Date: Thu, 26 Jul 2018 19:52:42 +0100

Will do, thanks!

On Thu, 26 Jul 2018 at 19:12, Laurent Vivier <address@hidden> wrote:

> Le 26/07/2018 à 19:58, Alex Bennée a écrit :
> >
> > Laurent Vivier <address@hidden> writes:
> >
> >> Le 26/07/2018 à 15:29, Alex Bennée a écrit:
> >>> I've slightly re-organised the check to more closely match the
> >>> sequence that the kernel uses in do_mmap().
> >>>
> >>> Signed-off-by: Alex Bennée <address@hidden>
> >>> Cc: umarcor <address@hidden>
> >>> ---
> >>>  linux-user/mmap.c | 14 +++++++++++---
> >>>  1 file changed, 11 insertions(+), 3 deletions(-)
> >>>
> >>> diff --git a/linux-user/mmap.c b/linux-user/mmap.c
> >>> index d0c50e4888..3ef69fa2d0 100644
> >>> --- a/linux-user/mmap.c
> >>> +++ b/linux-user/mmap.c
> >>> @@ -391,14 +391,22 @@ abi_long target_mmap(abi_ulong start, abi_ulong
> len, int prot,
> >>>      }
> >>>  #endif
> >>>
> >>> -    if (offset & ~TARGET_PAGE_MASK) {
> >>> +    if (!len) {
> >>>          errno = EINVAL;
> >>>          goto fail;
> >>>      }
> >>>
> >>>      len = TARGET_PAGE_ALIGN(len);
> >>> -    if (len == 0)
> >>> -        goto the_end;
> >>> +    if (!len) {
> >>> +        errno = EINVAL;
> >>> +        goto fail;
> >>> +    }
> >>
> >> Why do you check twice len?
> >> TARGET_PAGE_ALIGN() rounds up the value, so if it was not 0, it cannot
> >> be now.
> >
> > I was trying to follow the kernel style but I realise TARGET_PAGE_ALIGN
> > might be a different test compared to the kernel's PAGE_ALIGN(len) for
> > overflows:
> ...
> >       /* Careful about overflows.. */
> >       len = PAGE_ALIGN(len);
> >       if (!len)
> >               return -ENOMEM;
> >
>
>
> OK, so keep it but you should use ENOMEM, not EINVAL (and add a comment :)
> )
>
> Thanks,
> Laurent
>


-- 
Alex Bennée
KVM/QEMU Hacker for Linaro


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